(a) Field: Protective Coatings for Foods
(b) Prior Art
One of the prevalent problems existing in the bakery industry relates to the matter of staling as perceived by a firming of the food product due to moisture loss. In addition, in certain bakery type food products, and particularly in relation to donuts the starch portion is subject to retrogradation. Of the two types of problems the firming of the crumb due to the moisture loss as apparent drying contributes the major portion of the perceived staleness or hardening of baked or fried products. This problem is particularly acute when it comes to the matter of donuts and is so severe in yeast raised donuts as to bring about a situation in which yeast raised donuts have a very limited shelf life measured in terms of hours.
The baking industry has long sought a yeast raised donut which has a substantial shelf life measured in terms of days rather than hours. In order to mass produce donuts, whether of the cake or particularly the yeast raised type, and to allow for distribution in a normal manner and display in normal retail outlets, a period of days is required. To some extent cake type of donuts are not as subject to the severe crumb drying and perceived staleness as yeast raised donuts are. In an experiment, donuts were stored without coating or glaze in polyethylene bags. The donuts became firm and slightly mealy, which is a typical staling effect, after 2 to 3 days but did not dry out, thus remaining edible. When the same experiment was repeated using the donuts which had a sugarwater-stabilizer glaze applied, the donuts firmed very rapidly and were unsatisfactory within 24 to 48 hours. The rapid firming was concluded to be due to moisture migration from the donut's crumb to the glaze coating.
The water content of a packaged multicomponent baked or fried product will migrate from the high vapor pressure components to low vapor pressure components until equilibrium is reached. The vapor pressure, which can be determined individually for each component, is controlled by the amount of water, the amount of soluble solids and the amount of water binding agents. In the case of a yeast raised glazed donut, the glaze is a saturated sucrose solution having a relatively low vapor pressure, while the yeast raised donut has a relatively high vapor pressure due to the lack of appreciable soluble solids (low initial sugar much of which is metabolized), relatively high water content and a minimum of water binding ingredients. The overall effect is a rapid moisture migration from the crumb through the surface of the donut to the glaze which not only dries, and therefore firms the crumb, but also supersaturates the glaze solution and leads to a breakdown of the glaze.
The glaze breakdown mechanism may be described as follows: The glaze consists of small sucrose crystals (powdered sugar) held together and bonded to the donut surface by a saturated sucrose solution (syrup). The ratio of sucrose crystals to syrup controls the firmness, the opacity, and the eating character of the glaze. The major difference between a glaze and a flat icing is a higher crystal to syrup ratio for the icing. As the moisture migrates from the donut crumb to the glaze the syrup is diluted and the sugar crystals are dissolved. When there is insufficient amount of solid sugar crystals left to hold the glaze intact and when the syrup phase becomes predominant, the glaze liquifies, runs off, soaks into the product, sticks to the wrapper and is characterized by the term known in the art as glaze breakdown.
The interpositioning of a water barrier between the surface of the donut and the glaze would restrict moisture migration and thus prevent the donut crumb from drying out and protect the glaze from breakdown.
Use of water barriers on food products including baked and fried products is now new. "Crystal Gum", a tapioca dextrin sold by National Starch and Chemical Corporation, Bridgewater, N.J., has been utilized as an aqueous dextrin sucrose spray applied to baked cake and pie products prior to icing or glazing to extend the shelf life of the products and to minimize glaze and icing breakdown. In addition, there are many literature and patent references describing the use of coatings on food products to reduce moisture loss or migration. Most such work has been done on meat products which are, of course, processed and cooked prior to consumption. In fruit the coating is removed with the peeling and thus does not interfere with the eating properties. On non-porous semi-smooth products such as nuts, candies and the like, various coatings of various carefully controlled thicknesses have been utilized for a similar purpose.
None of the prior art coating materials or methods have been satisfactory in accomplishing the desired goals of a shelf stable yeast raised glazed donut. It must be understood that donuts bring about particularly acute conditions which require a special composition and coating technique in order to achieve a satisfactory product. The water barrier or precoat applied to a freshly fried donut of either the cake or yeast raised type, but particularly the yeast raised type, must be an effective water barrier to the very porous donut surface and at the same time must not detract from the eating qualities of the donut. The coating must have a substantial amount of flexibility so that it does not crack or chip during subsequent glazing, icing or packaging of the product.
With these general requirements in mind, the following is a review of the available prior art literature and patents as compared to the specific compositions and processes described hereinafter for producing a satisfactory water barrier on a baked or fried food product with particular emphasis on the critical requirements for a glazed yeast raised donut. In an article by Allen, L., et al, "Edible Corn-Carbohydrate Food Coating", I, Food Technology at Pg. 99, November 1963 and II, Food Technology at Pg. 104 November 1963, there is a description of corn starch or corn sugars in combination with alginates used as moisture and oxygen barrier films on meat products. The articles specifically refer to an adverse flavor effect which would be amplified if the same type of coating or film were to be applied to a yeast raised donut.
In an anonymous article--"Outlook for Grapes: Better Raisins", Canner Packer, at Pg. 52, March 1977, it is taught that protein coatings from egg or soy have been found to effectively reduce moisture loss in raisins. Such protein coatings have been evaluated and they have been found to have very poor water barrier properties when applied to a porous donut surface. In addition they were found to be too difficult to apply for commercial operations.
An article by Ayres, J. C., "Use of Coating Materials", Food Technology, at Pg. 512, Sept. 1959, there is a listing of earlier precoat work and a teaching that an agar-glycerol solution or diacetyl triglycerides, when used as meat coatings, are for the purpose of primarily to retard microbiological growth. The films described are strippable and the moisture barrier properties of the agar films were minimal. The diacetyl triglycerides are described as having good moisture barrier properties, however evaluation of that type of coating on yeast raised donuts based on our experiences with fat based coatings would raise severe thickness control problems and the eating properties of these films on a porous donut surface would be unacceptable. Furthermore the heat stability of the diacetyl triglyceride coating would not be satisfactory in view of the subsequent glazing operation.
In Bauer, C. D., et al U.S. Pat. No. 3,406,081, Oct. 15, 1968, there is a description of a lipid meat coating applied as water in oil emulsion. The application as an emulsion would eliminate the normally brittle character of straight lipid coatings. The precoating of this invention is also applied as a water in oil emulsion and it may be its use as an emulsion which allows satisfactory weight control and the excellent flex properties of the precoat compositions of this invention.
In Bauer, C. D., U.S. Pat. No. 3,483,004, there is a teaching of the addition of thermal gelling methylcellulose to the composition described in Bauer, et al, U.S. Pat. No. 3,406,081 for the purpose of preserving the coating during cooking of the meat. This is unrelated to the composition and methods of this invention.
In Canonne, J. E., U.S. Pat. No. 4,010,283, there is a description of a use of a gum arabic coating. Such coatings were evaluated during the course of our work and it has been found that dextrin coatings are superior to gum arabic coatings. However, a dextrin coating alone was unsatisfactory for yeast raised donuts and accordingly it is highly unlikely that gum arabic coatings would be satisfactory for yeast raised donuts.
In Clark, W. L. "Hot Melt Transparent Peelable Coating for Food", Food Technology at Pg. 105, October 1965, there is described an acetylated monoglyceride-cellulose acetate butyrate coating. Cellulose acetate butyrate was added to overcome lack of transparency and to satisfy the need for plasticizers when straight acetylated monoglycerides are used. The coating is a peelable film and would not be applicable to a porous baked food product. Additionally transparency is not a problem with a precoat composition of this invention and satisfactory flexibility of the coating has been achieved without the use of the special additives taught in this article.
In the article by Feuge, R. O., "Acetoglycerides-New Fat products of Potential Value to the Food Industry" Food Technology at Pg. 314, June 1955, there is discussion of properties and potential use of acetylated monoglycerides. In this article, the use of acetylated monoglycerides as potential coating agents is addressed to their waxy character an while the author refers to potential use as coatings on baked products, no details are given.
In Hamdy, M. M. U.S. Pat. No. 3,471,304, there is the teaching of utilizing a combination of acetylated monoglyceride and ethyl cellulose for the purpose of overcoming negative qualities of either component when used separately as a coating material.
In Hullinger, C. H. "Starch Film and Coating", Cereal Science Today at Pg. 508, October 1969, there is discussion of starch films which, since they have poor water barrier properties, are not suitable for use in accordance with the teaching of this invention.
In the article by Jokay, L. "Development of Edible Amylaceous Coatings For Foods", Food Technology at Pg. 12, August 1967, there is discussed the advantages of hydroxypropyl derivatives of amylose starch over other starch coating materials. This type of coating does not have good moisture barrier properties. In addition this article does, however, discuss various prior art coating application equipment and contains literature references to such prior art coating equipment.
In the article by Lazarus, C. R., "Evaluation of Calcium Alginate Coating", Journal of Food Science at Pg. 639, Vol. 41 (1976), there is discussed the in situ precipitation of calcium alginate to form a film. Such films were evaluated during a course of our work and were found to be unacceptable since they have gel like eating properties when applied to donuts, which materially interferes with the eating qualities of the donuts.
In Lowe, E. "Continuous Raisin Coater", Food Technology at Pg. 109, Nov. 1963, there is a discussion of an acetylated-lipid coating. This type of coating was tested during our work on donuts and it was found that the porosity of the donut, coupled with the inability to apply a thin yet continuous coating, limited their use either due to unsatisfactory eating character or to poor moisture barrier properties.
In the article by Myer, R. C., "Edible Protective Coating for Extending the Shelf Life of Poultry", Food Technology at Pg. 146, February 1959, there is a description of a agar-glycerine and carrageenan coating utilized as moisture barriers on poultry. Such a coating would have a tendency to produce gel like eating properties when applied to porous products such as donuts and accordingly would be unsatisfactory.
In an article by Miers, J. C. "Pectinate and Pectate Coating", Food Technology at Pg. 229, June 1953, there is a description of calcium precipitated pectinate coatings. (See also Swenson, H. A. "Pectinate and Pectate Coating" Food Technology at Pg.. 232, June 1953). Such coatings were investigated during the course of our work and were found to have unacceptable gel-like eating properties.
An article by Murray, D. G., "Low DE Corn Starch Hydrolysates," Food Technology at Pg. 32, March 1973, describes the general purpose of low DE corn syrup solids and its successful use of such a moisture barrier coating on fruits and nuts. We have found that such low DE solids alone do not provide sufficient moisture protection when applied to donuts but are one of the components of the composition of matter of this invention, all of which together have a synergistic result of producing a satisfactory precoat water barrier on donuts.
In an article by Newman, A. A., "The Acetoglycerides", Food Manufactures at Pg. 525, November 1962, there is an overview of acetylated monoglycerides similar to the description contained in the article by Feuge referred to above. The list at the end of the description of the text makes no reference to the use of such materials on baked goods.
In an article by Paredes-Lopez, O. "Use of Coating of Candelilla Wax for the Preservation of Limes", J. Sci. Fd. Agric. at Pg. 1207, Vol. 25, 1974, there is a description of the application of a wax emulsion as a moisture barrier to limes. This would have similar limitations to its use in conjunction with yeast raised donuts as the products referenced in the Bauer, U.S. Pat. No. 3,406,081, described above.
In Stemmler, M., U.S. Pat. No. 3,851,077, there is described the use of acetylated monoglyceride as a protective coating on fresh meat. As described in conjunction with the Lowe article referenced above, this type of coating is not satisfactory on donuts.
The Ukai, N., U.S. Pat. No. 3,997,674 describes a coating composition comprising an aqueous solution or dispersion of a water soluble polymer and a hydrophobic (fat or wax type material) component stabilized by the use of a suitable emulsifier. At Column 7, lines 10-30 it is stated that the ratio of the components is critical for the specific use of the composition, described to preserve relatively low porous materials such as eggs, apples, grapefruit and the like. A similar ratio of the components of the unique composition of this invention are also critical to the use on baked or fried products. The Ukai patent lists water soluble polymers in Column 8, lines 35-40, which include hexosans, starches, etc. One of the preferred materials in the compositions of matter of this invention is a low DE corn syrup solid, which is a hexosan. In Column 8, lines 52-57 there is a list of the hydrophobic substances including lipids and waxes which may be used.
In the article by Walters, G. "Stabilized Raisins for Dry Cereal Products," Food Technology at Pg. 236, May 1961, there is described the use of beeswax dispersed in vegetable oil as a moisture coating. While the oil reduces the moisture barrier properties of the wax and should reduce the problems of applying a thin continuous coat of the wax, a principle difficulty which we have found in our work limited the use of waxy materials on donuts, we have found that this specific teaching does not produce a satisfactory precoat water barrier on donuts.
In Werbin, D. U.S. Pat. No. 3,526,515, there is a description of coating of baked foods with a blend of oil or hydrogenated shortening and a high melting fat. We have found that such a coating is not satisfactory for the baked and fried food products of this invention.
The above referenced literature and patents describe the scope and content of the prior art and in many instances the same or similar compositions were tested or evaluated as a precoating of the water barrier type for baked and fried type and specifically yeast glazed raised donuts. None were found to have the combination of properties required to produce a satisfactory yeast raised glazed donut having an extended shelf life which still retained satisfactory eating properties. Thus, while the use of an edible coating to protect a food product from moisture loss is well known none of those described in the prior art have been found to solve the problem as is further indicated by the fact that an extended shelf life yeast raised glazed donut did not exist as a satisfactory commercial product prior to this invention. Other teachings of the prior art such as the use of an overwrap on the food products with a suitable packaging film to reduce moisture migration as taught by the prior art does not prevent moisture migration between the various components of a multicomponent food product and hence is unsatisfactory.
Accordingly our work was directed to providing an edible coating which could be applied in such a manner as to isolate one product component from another, and in this specific instance, to isolate the donut from its glaze with a water barrier to prevent or materially delay moisture migration. The prior art teachings of coatings in the literature which are removed with the peels or skin; which are removed during the processing such as baking or reheating prior to consumption; or as are applied to relatively non-porous firm products such as apples, nuts and the like which permit a very thin film to be applied are not directly related to our situation, which presented a problem which required the solution first provided by this invention.
In the case of a baked or fried food product the surface of the food is very porous and in many cases is soft and flexible. When coatings such as waxes or triglycerides are applied to such a surface two major problems are encountered. The first is the inability to apply a thin coating which will provide the water barrier protection, yet not have thick spots which would interfere with the normal eating properties. The second problem is the ability to provide a coating which has the required flexibility or elasticity so that it will not chip, crack, etc. when the food product is slightly deformed during handling or transit.